Electrode probes for inserting into a body to record electrical signals from and to stimulate the heart are generally known in the prior art. Such probes are inserted into the body past the pharynx and into the esophagus or trachea into close proximity to the heart. Such probes may be used either for diagnosis or for therapeutic applications. For diagnosis, the heart can be monitored, and for therapeutic purposes, an electrical stimulus applied to the heart via the probe at any instant, as appropriate.
Stethoscopes for monitoring heart sounds are also well-known. The most commonly known type is an external device which consists simply of a pair of ear pieces and a tube leading to each ear piece which transmits heart sounds from a pick-up, which is usually placed in proximity to the heart of the patient. Stethoscope pick-ups for insertion into a patient's esophagus, trachea or pharynx are also known. If inserted into the esophagus, these stethoscopes may be a long hollow tube having a closed distal end and one or more openings positioned along the length of the tube, to transmit heart sounds from inside the esophagus through the interior of the tube. The openings are typically covered with a thin film, which is sealed to the tube, to prevent body fluid from entering the stethoscope. The physician's ear pieces are connected to a Y-cap at the proximal end of the tube, so that the physician can monitor the heart sounds inside the esophagus.
Other types of stethoscopes for insertion through the mouth or nose are also well known, such as ones which use a microphone or other transducer to convert the heart sounds into electrical signals and wires to conduct the electrical signals from the transducer to outside of the patient for monitoring by attending personnel. U.S. Pat. No. 4,088,138 discloses a cardiac resuscitator and monitoring apparatus having an oropharyngeal airway for insertion into the mouth of a patient who has undergone a suspected heart attack. The airway has an electrical micro-phone at its end and electrodes for giving an indication of electrical heart activity. An electrical signal to stimulate the heart, such as a defibrillating or pacing pulse, may be provided between these electrodes or a separate electrode on the airway, and another electrode applied elsewhere to the patient's body.
It is important in such devices to position such active electrodes as closely to the heart as possible. Because the esophagus comes in close proximity to the left atrium, less current is required to pace the heart at this location compared to other locations. This is advantageous for a number of reasons, one of which is the reduced pain and hazard to the patient. Although the current levels required to pace the ventricles are high, it should be understood that such electrodes may also be used for ventrical stimulation in the event of some form of atrio-ventricular block inhibiting the normal conduction pathways of the heart. It is usually intended to apply the signal to the atria, and not the ventricles, to avoid inducing undesired cardiac reactions, such as ventricular fibrillation.
It is also desirable to make probes for insertion into the body as inexpensively as possible so that they can be disposed of after each use rather than requiring sterilization. That way, a new probe can be used for each patient without risk of infection.